Some pyrrolobenzodiazepines (PBDs) have the ability to recognise and bond to specific sequences of DNA; the preferred sequence is PuGPu. The first PBD antitumour antibiotic, anthramycin, was discovered in 1965 (Leimgruber, et al., J. Am. Chem. Soc., 87, 5793-5795 (1965); Leimgruber, et al., J. Am. Chem. Soc., 87, 5791-5793 (1965)). Since then, a number of naturally occurring PBDs have been reported, and over 10 synthetic routes have been developed to a variety of analogues (Thurston, et al., Chem. Rev. 1994, 433-465 (1994)). Family members include abbeymycin (Hochlowski, et al., J. Antibiotics, 40, 145-148 (1987)), chicamycin (Konishi, et al., J. Antibiotics, 37, 200-206 (1984)), DC-81 (Japanese Patent 58-180 487; Thurston, et al., Chem. Brit., 26, 767-772 (1990); Bose, et al., Tetrahedron, 48, 751-758 (1992)), mazethramycin (Kuminoto, et al., J. Antibiotics, 33, 665-667 (1980)), neothramycins A and B (Takeuchi, et al., J. Antibiotics, 29, 93-96 (1976)), porothramycin (Tsunakawa, et al., J. Antibiotics, 41, 1366-1373 (1988)), prothracarcin (Shimizu, et al, J. Antibiotics, 35, 972-978 (1982); Langley and Thurston, J. Org. Chem., 52, 91-97 (1987)), sibanomicin (DC-102)(Hara, et al., J. Antibiotics, 41, 702-704 (1988); Itoh, et al., J. Antibiotics, 41, 1281-1284 (1988)), sibiromycin (Leber, et al., J. Am. Chem. Soc., 110, 2992-2993 (1988)) and tomamycin (Arima, et al., J. Antibiotics, 25, 437-444 (1972)). PBDs are of the general structure:

They differ in the number, type and position of substituents, in both their aromatic A rings and pyrrolo C rings, and in the degree of saturation of the C ring. In the B-ring there is either an imine (N═C), a carbinolamine (NH—CH(OH)), or a carbinolamine methyl ether (NH—CH(OMe)) at the N10-C11 position which is the electrophilic centre responsible for alkylating DNA. All of the known natural products have an (S)-configuration at the chiral C11a position which provides them with a right-handed twist when viewed from the C ring towards the A ring. This gives them the appropriate three-dimensional shape for isohelicity with the minor groove of B-form DNA, leading to a snug fit at the binding site (Kohn, In Antibiotics III. Springer-Verlag, New York, pp. 3-11 (1975); Hurley and Needham-VanDevanter, Acc. Chem. Res., 19, 230-237 (1986)). Their ability to form an adduct in the minor groove, enables them to interfere with DNA processing, hence their use as antitumour agents. The synthesis of the compounds has been reviewed in Thurston, D. E., et al., Chem. Rev., 1994, 94, 433-465 and Thurston, D. E., et al., Chem. Rev., 2011, 111, 2815-2864.
The large majority of antibiotics in current clinical use are derived from bactericidal or bacteriostatic molecules produced as secondary metabolites by microbes, predominantly those belonging to the moulds and actinobacteria. Screening has identified molecules such as the pyrrolobenzodiazepines (PBDs) tomaymycin, anthramycin and DC-81 that exerted potent antibacterial activity against human pathogens through a capacity to bind to DNA; some of these compounds have potential as cancer chemotherapeutics but a high degree of cytotoxicity has rendered them unattractive as antibacterial antibiotics in comparison to other classes of compound.
However, the evolution of multidrug-resistant pathogens capable of rapid and efficient horizontal transmission of genes encoding antibiotic resistance determinants has facilitated the erosion in a relatively short timeframe of much of the therapeutic value of frontline antibacterial chemotherapeutic agents. Increasing multidrug resistance in Gram-negative pathogens such as Pseudomonas aeruginosa and Acinetobacter baumannii has forced the reappraisal of colistin for systemic use; this polymyxin antibiotic, discovered more than fifty years ago and until recently considered too toxic for non-topical use, is now widely used systemically due to the limited therapeutic options available for these infections.
A number of conjugates of PBD with pyrroles and imidazoles have been reported, such as:
where n=1-3 (Damayanthi, Y., et al., Journal of Organic Chemistry, 64(1), 290-292 (1999));
where n=1-3 and
where n=1-2 (Kumar, R. and Lown, J. W. Oncology Research, 13(4), 221-233 (2003)); Kumar, R., et al., Heterocyclic Communications, 8(1), 19-26 (2002));
where n=1-4, (Baraldi, P. G., et al., Journal of Medicinal Chemistry, 42(25), 5131-5141 (1999));
where n=3, (Wells, G., et al., Proc. Am. Assoc. Canc. Res., 2003, 44, 452).
In WO 2005/085177, some of the present inventors disclosed amino acids comprising a biaryl core that could have useful properties in DNA binding.
The inventors have now discovered that the PBD conjugates of the prior art may be modified in order to achieve improved properties, particularly antibacterial properties. In particular, the present invention relates to the incorporation of an amino acid residue containing a 5-membered heterocyclic group in combination with an arylene based amino acid residue in a PBD conjugate results in highly effective compounds.
A first aspect of the present invention provides a compound of formula I:
or a salt or solvate thereof, wherein:the dotted double bond indicates the presence of a single or double bond between C2 and C3;
R2 is selected from —H, —OH, ═O, ═CH2, —CN, —R, OR, halo, dihalo, ═CHR, ═CHRR′, —O—SO2—R, CO2R and COR;
R7 is selected from H, R, OH, OR, SH, SR, NH2, NHR, NRR′, nitro, Me3Sn and halo; where R and R′ are independently selected from optionally substituted C1-7 alkyl, C3-20 heterocyclyl and C5-20 aryl groups;
R10 and R11 either together form a double bond, or are selected from H and QRQ respectively, where Q is selected from O, S and NH and RQ is H or C1-7 alkyl or H and SOxM, where x is 2 or 3, and M is a monovalent pharmaceutically acceptable cation;
A is selected from A1, A2, A3, A4 or A5:
WhereX1 and Y1 are selected from: CH and NH; CH and NMe; N and NMe; CH and S; N and S; N and O; and CH and O, respectively;X2 and Y2 are selected from: CH and NH; CH and NMe; N and NMe; CH and S; N and S; N and O; and CH and O, respectively;Z1 is selected from O and S;Z2 is selected from CH and N;F is selected from a single bond and -(E-F1)m—;each E is independently selected from a single bond, and —C(═O)—NH—;each F1 is independently a C3-20 heteroarylene group;m is 1, 2 or 3;G is selected from hydrogen, C1-4alkyl, —C(═O)—O—C1-4alkyl, —(CH2)n—C3-20 heterocycloalkyl, and —O—(CH2)n—C3-20 heterocycloalkyl group, and each n is 0-4;provided that A2 is not A2′:
where X1 and Y1 of A2′ are selected from: CH and NMe; COH and NMe; CH and S; N and NMe; N and S, respectively; andprovided that A3 is not A3′:
where X2 and Y2 of A3′ are selected from: CH and NMe; COH and NMe; CH and S; N and NMe; N and S, respectively;B in A2′ and A3′ is either a single bond or:
where X and Y of B1 are selected from: CH and NMe; COH and NMe; CH and S; N and NMe; N and S, respectively; andR1 is C1-4 alkyl.
A second aspect of the present invention provides a method of synthesis of a compound of formula I.
A third aspect of the present invention provides a pharmaceutical composition comprising a compound of the first aspect of the invention and a pharmaceutically acceptable carrier or diluent.
A fourth aspect of the present invention provides a compound of the first aspect of the invention for use in a method of therapy.
A fifth aspect of the present invention provides the use of a compound of the first aspect of the invention in the manufacture of a medicament for the treatment of a bacterial infection. This aspect also provides a compound of the first aspect for use in a method of treatment of a bacterial infection.
A sixth aspect of the present invention provides a method of treatment of a patient suffering from a bacterial infection, comprising administering to said patient a therapeutically acceptable amount of a compound of the first aspect or a composition of the third aspect.
In the fourth to sixth aspects of the invention, the compound of the invention may be administered alone or in combination with other treatments, either simultaneously or sequentially dependent upon the condition to be treated. In the third aspect of the invention, the pharmaceutical composition may comprise one or more (e.g. two, three or four) further active agents.